Nisyros is a volcanic Greek island and municipality located in the Aegean Sea. It is part of the Dodecanese group of islands, situated between the islands of Kos and Tilos. Its shape is approximately round, with a diameter of about 8 km. Several other islets are found in the direct vicinity of Nisyros, the largest of which is Gyali. Nisyros, with fewer than 1000 permanent inhabitants, is famous for having the only active volcano in Greece together with Santorini. The island is essentially a volcanic cone with a large collapsed caldera in the center. It is possible to walk into the volcanic crater and view the smoking fumaroles at close hand.